1. Field of the Invention
The present invention relates to a heavy oil emulsion fuel composition. More particularly, it is concerned with an aqueous emulsion fuel composition comprising (a) a heavy oil, (b) water, (c) a surfactant and (d) at least one component selected from the group consisting of water-soluble compounds having in its molecule two or more hydroxyl groups, monohydric alcohols having 6 or more carbon atoms, and mixtures thereof. The emulsion fuel composition of the present invention has excellent storage stability and lesspollutive property.
2. Description of the Related Art
In recent years, there has been a demand for the development of a substitute fuel for petroleum, which is widely used as an energy source, due to the decrease in the petroleum reserve and its accompanying rise in price. Under the above-described circumstances, studies have been made to convert heavy oils, such as oil sand, bitumens, distillation residues of petroleum and asphalt, into fuel.
However, these heavy oils are usually an oleaginous material containing about 60 to 70%, and in some cases, more than 70% of a heavy fraction having a boiling point of 420.degree. to 450.degree. C., and in some cases, higher than 450.degree. C. This heavy fraction of the heavy oils is usually a vacuum distillation residue, and as such, do not flow or have a viscosity as high as tens of thousands of centipoises or more. For this reason, when the heavy oils are used as a fuel, heating to a temperature as high as 280.degree. to 300.degree. C. is required, or else problems occur in handling, atomization, etc., as well as problems such as the clogging of the piping, etc., of the combustion boilers. As described above, the heavy oils are very difficult to use as a fuel.
In order to solve these problems, U.S. Pat. Nos. 4,249,554 (published on Feb. 10, 1981; Assignee: Conoco Inc.), 4,776,977 (published on Oct. 11, 1988; Assignee: The British Petroleum Company p.l.c.), 4,923,483 (published on May 8, 1990; Assignee: Intevep,S. A.), 4,934,398 (published on Jun. 19, 1990; Assignee: The British Petroleum Company p.l.c.), and 5,024,676 (published on Jun. 18, 1991; Assignee: Kao Corporation and Mitsubishi Jukogyo Kabushiki Kaisha), and Japanese Patent Publication-A No. 3-97,788 (published on Apr. 23, 1991) propose emulsion fuels. These emulsion fuels, however, have the problem of poor storage stability, and are not satisfactory emulsion fuels.
In addition, these heavy oils exhibit higher residual carbon and nitrogen contents than those of gas oil, kerosine and fuel oil generally used as a fuel. Therefore, when these heavy oils are used as a fuel, a serious problem arises in that the contents of soot and dust and nitrogen oxides in the exhaust gases are increased.